Formation of dihydrofuran derivatives by intramolecular substitution of the manno adducts formed by Michael reaction of a 1-O-acetyl-3-C-nitro-2-enopyranose derivative with 2,4-pentanedione and dibenzoylmethane

Article abstract of DOI:10.1016/0008-6215(91)84050-O

Michael reaction of 1-O-acetyl-4,6-O-benzylidene-2,3-dideoxy-3-C-nitro-α-D-erythro-hex-2-enopyranose with 2,4-pentanedione afforded two cyclized products, together with adducts having the α-D-gluco and α-D-manno configurations.The dihydrofuran structures of the cyclized products were determined from spectral data, supported by semi-empirical molecular orbital(AM1) calculations.Cyclization occurred from the manno adduct through nucleophilic expulsion of the anomeric acetoxyl group by an enolate generated from the C-2 substituent.Such a proposed intramolecular SN2 mechanism was supported by a similar reaction with dibenzoylmethane.